<html>

<head>
    <!-- include Vue 2.x -->
    <script src="https://cdn.jsdelivr.net/npm/vue@^2"></script>
    <!-- include vue-treeselect & its styles. you can change the version tag to better suit your need. -->
    <script src="https://cdn.jsdelivr.net/npm/@riophae/vue-treeselect@0.0.38/dist/vue-treeselect.min.js"></script>
    <link rel="stylesheet"
        href="https://cdn.jsdelivr.net/npm/@riophae/vue-treeselect@0.0.38/dist/vue-treeselect.min.css">
</head>

<body>
    <div id="app">
        <treeselect v-model="value" alwaysOpen="true"    show-count="true" :multiple="true" :options="options" :appendToBody="appendToBody" />
    </div>
</body>
<script>
    // register the component
    Vue.component('treeselect', VueTreeselect.Treeselect)

    new Vue({
        el: '#app',
        data: {
            // define default value
            value: null,
            appendToBody: true,
            // define options
            options: [{
                id: 'a',
                label: 'a',
                children: [{
                    id: 'aa',
                    label: 'aa',
                }, {
                    id: 'ab',
                    label: 'ab',
                }],
            }, {
                id: 'b',
                label: 'b',
            }, {
                id: 'c',
                label: 'c',
            }],
        },
    })
</script>

</html>